Field of the Invention
The present invention relates to a method of preparing iron oxide nanoparticles, and more particularly, to a method of preparing iron oxide nanoparticles, iron oxide nanoparticles prepared thereby, and an anode material including the iron oxide nanoparticles.
Description of the Related Art
Recently, as issues, such as the depletion of fossil fuels and environmental destruction, have emerged, many researchers have devoted to develop alternative energies that may replace fossil fuels. As a kind of such alternative energies, a significant amount of research into secondary batteries that are applicable to various fields has been conducted.
The application fields of secondary batteries have been further expanded to batteries for vehicles and batteries for power storage as well as typical portable systems.
A secondary battery may be composed of a cathode, an anode, an electrolyte solution, and a separator, and among these, components that mostly affect the battery may be the cathode and the anode in which electrochemical reactions actually occur.
A graphite material has mainly been used as the anode due to its competitiveness in terms of stability, lifetime, and price. However, as high-capacity batteries, which may be used in electric vehicles and batteries for power storage, have been increasingly required, research into developing a new anode material having high theoretical capacity has emerged.
In line with such requirements, metal oxides have recently received attention as a high-capacity anode active material, and particularly, iron (III) oxide (Fe2O3) among these oxides has received attention as an anode material due to its high theoretical capacity (1007 mAh/g).
However, since capacity and cycle efficiency may decrease during a charge/discharge process when a particle diameter of the metal oxide is large (>1 μm), research into preparing nanometer-sized iron oxide particles by various chemical syntheses has continued.
As a synthesis method of the iron oxide nanoparticles, a method has been known, in which a ferrous hydroxide (Fe(OH)2) aqueous solution, which is prepared by adding sodium hydroxide to a ferric salt aqueous solution, is irradiated with ultrasonic waves.
However, with respect to a typical synthesis method of iron oxide, difficult synthesis conditions (inert atmosphere) must be maintained and an expensive high purity raw material must be used. In addition, since the particles obtained by the irradiation of ultrasonic waves may not be uniform and may have poor crystallinity, the application range thereof may be narrow. Also, since it takes a long time to irradiate with ultrasonic waves, mass production may be impossible.
Furthermore, since iron (III) oxide nanoparticles prepared by a typical method may be difficult to be prepared as nanoparticles having a fine and uniform particle size, cracks may occur in an electrode due to volume expansion and shrinkage of the electrode during a charge/discharge process. Thus, capacity loss is high and cycle efficiency rapidly decreases.
Therefore, development of a method of preparing iron oxide nanoparticles is urgent, in which limitations of a typical preparation method of iron oxide nanoparticles, such as complex process and long preparation time, may be addressed, particle diameter and shape of powder may be uniformly controlled, and simultaneously, capacity loss may be low even during numerous charge/discharge processes.